This application is based on Japanese Patent Application No. 87551/1999 filed on Mar. 30, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a three-dimensional information measuring apparatus for obtaining data about a profile of an object or a distance to an object.
2. Description of the Prior Art
A non-contact type three-dimensional information measuring apparatus which enables rapid measurement compared with a contact type is used for data input into a CG system or a CAD system, physical measurement, visual sense of a robot or other applications.
A slit light projection method (also referred to as a light cutting method) is known as the measurement method suitable for the non-contact type three-dimensional information measuring apparatus. This method is a method for obtaining a distance image by scanning an object optically, and is one of active measurement methods for taking an image of an object by irradiating a reference light beam. The distance image is a set of pixels that indicate three-dimensional positions of plural parts of the object. In the slit light projection method, a slit light beam having a slit-like section is used as the reference light beam and is deflected in the width direction of the slit for line sequential scanning. The longitudinal direction of the slit is the primary scanning direction, and the width direction of the slit is the secondary scanning direction. At a certain time point in the scanning, a part of the object is irradiated and an emission line that is curved in accordance with bumps and dips of the irradiated part appears on a light reception surface of the imaging system. Therefore, a group of three-dimensional input data that determine the shape of the object can be obtained by sampling intensity of each pixel of the light reception surface periodically in the scanning.
The size of the object that can be measured depends on an angle of view and a distance to the object (a shooting distance) for taking the image. If an auto focus (AF) is performed, a distance to the object is measured before taking the image. In addition, there is a three-dimensional information measuring apparatus that has a function for setting the irradiation angle range of the slit light beam to an optimal value automatically in accordance with the measured distance to the object and the angle of view at that time point.
In the conventional three-dimensional information measuring apparatus, a light beam entering the imaging lens is extracted by a half mirror and is led to an AF sensor for measuring a distance to the object. This is so-called a TTL distance measuring method in which the direction of measuring the distance and the direction of the light reception axis for taking the image are substantially the identical.
In the above-mentioned measurement of distance to the object, it is considered to use an AF sensor that is disposed at the position separate from the imaging lens. Thus, a flexibility of the design of the imaging lens can be enhanced. In addition, using an active type sensor that is used commonly for a compact silver-halide film camera as the AF sensor, the three-dimensional information measuring apparatus can be inexpensive.
However, if the AF sensor is arranged so that the direction of measuring the distance is parallel with the direction of the optical axis for taking the image in the same way as the compact silver-halide film camera, the following problem comes up. When the size of the object of three-dimensional data input is smaller than a predetermined value, it is difficult to measure the distance to the object with a predetermined accuracy regardless of whether the position of the object is near or far. This is caused because the position of the AF sensor is separated from the optical axis by at least the distance corresponding to the diameter of the imaging lens. Another problem is that the rate of the misregistration between the optical axis and the AF sensor with respect to the view of imaging varies substantially in accordance with the distance to the object, and an adjustment of a focal point has a tendency to become incorrect when the distance to the object becomes short.
The object of the present invention is to enable the three-dimensional data input of a small object when a distance measuring sensor is disposed at the external of the imaging lens. Another object is to make uniformity of influence of the misregistration between the imaging lens and the distance measuring sensor over the whole range of distance in which the image can be obtained for the three-dimensional data input.
A three-dimensional information measuring apparatus for obtaining data about a position of an object according to the present invention comprises an imaging sensor, an imaging optical system for leading an optical image of the object to the imaging sensor, and a distance measuring module for measuring a distance to the object in the direction inclining a predetermined angle with respect to the optical axis of the imaging optical system.